This invention relates to a slot wedge assembly for a dynamoelectric machine, and in particular it relates to an improved wedge assembly for retaining conductors in stator slots in a dynamoelectric machine.
In larger dynamoelectric machines there is normally a stator core formed of a stack of laminations having slots. When the laminations are assembled in a stack the individual slots are aligned to form axially extending, radial slots which have a slot opening or slot mouth at a radially inner circumference of the stator core annulus. Stator bars or conductors are installed in these slots and they must be held firmly in place against mechanical and electromagnetic forces which tend to cause movement. The slots are usually made with a dove-tail adjacent the slot mouth or slot opening, and a key or wedge assembly of mating configuration with the dove-tail is pressed into the dove-tail to close the slot. Shims and/or springs are often used between the conductors and the slot closure or wedge assembly to prevent movement of the conductors.
Conductors used in larger dynamoelectric machines usually have a jacket formed of a thermosetting resinous material impregnating a porous material and this is cured to a hard state, forming the insulating jacket around the conductor. In addition, there may be portions of the jacket coated with a partially conducting resilient elastomer to reduce the possibility of corona discharge between the conductors and the slot walls. When these conductors are first installed they are very firmly wedged into their slots and are satisfactorily restrained against movement. However, with time the possibility of decreasing restraining forces has been a problem. Repeated thermal cycling may permit some flowing of the jacket surrounding the conductors or there may be some shrinkage. In larger machines the conductors may carry large currents and the electromagnetic forces can be quite strong. These factors may aid in decreasing the restraining forces. To reduce the possibility of restraining forces decreasing unacceptably with time, it has been usual to use a spring force between the wedge assembly and the conductors.
Various configurations and arrangements have been devised to provide a spring force between the wedge assembly and the conductors. For example, it is known to use "ripple springs", that is, strips of spring metal formed with transverse ripples, placed to exert a force between the slot closure and the conductors. U.S. Pat. No. 3,909,931 - LAMBRECHT, issued Oct. 7, 1975 and No. 3,949,255 - BROWN and HAWLEY, issued Apr. 6, 1976, are examples of arrangements using this form of spring.
Another arrangement to provide a spring force between slot closure or wedge assembly and conductor is described in Canadian Pat. No. 1,095,108 - FERGUSON, issued Feb. 3, 1981. In this arrangement the spring extends along the slot with a curvature that is transversely oriented with respect to slot length so that it exerts its force along the length of the slot rather than across it. This spring is preferably made of layers of glass cloth impregnated with a curved thermosetting polyester resin.
The known spring arrangements, while they maintain a restraining force over an increased period of time, require a separate spring in the wedge assembly. The installation and maintenance would be easier if the separate spring could be eliminated while the spring force is retained.